Earplugs are used in various situations where protection against or alleviation of outside noise is required. In many situations there is a need for earplugs that are small, easy to use and affordable and, at the same time, effective in cancelling noises of different frequencies.
For example, cabin noise in airplanes is a phenomenon of fairly low frequencies where the peak is around 70 Hz, and the peak cabin noise at this frequency can be as high as 90 dB. This can be especially stressful and annoying when trying to sleep during a flight, or when simply trying to relax in a noisy environment.
Also music, speech or other noise coming through walls of an apartment may create a stressful environment where attenuation of the unwanted noise is needed, especially during night time when the person suffering from the noise is trying to sleep or rest. The attenuation of such noise of fairly low frequencies would be desired.
The audio environment inside a motorcycle helmet of a motorist whilst riding has similar conditions, as well, which makes listening to radio and/or music while riding uncomfortable, as unwanted noise frequencies interfere or disrupt those of the desired audio input.
Earplugs with passive noise reduction are typically relatively cheap, simple structures made of foam plastic, memory foam, silicone, coated wax or other such malleable materials suitable for moulding in one's hands and inserting into one's ear canal where they subsequently expand to fill out the ear canal to passively reduce the noise reaching the audio organs. They do not offer very good protection against noise in the above-described situations. While their noise reduction capability increases with noise frequency, it is not particularly good at low frequencies.
On the other hand, active noise cancellation (ANC) works well at low frequencies, utilising a microphone for detecting noise, a Digital Signal Processor (DSP) or other signal processing equipment such as an analogue filter for processing the noise, and a speaker for producing antinoise cancelling the noise to be controlled. Commonly, ANC solutions utilise feedback or feed-forward topologies, or a combination of the two. In most embodiments ANC devices work well for noise with frequency 1 kHz or less. In addition, the present solutions for active noise cancellation can be relatively expensive and/or so cumbersome in their size and design that their use in the above-described situations is not feasible. Typically, ANC solutions are utilised in earplugs or headphones designed particularly for listening to music, and they are not suitable for sleeping or resting one's head against a pillow or a headrest.
Large earphones, or earplugs that extend from the ear beyond the tragus, antitragus and antihelix of the ear can well be worn when the user is standing, sitting or lying on his/her back. However, such earphones or earplugs are uncomfortable to wear when lying sideways or wearing head protection such as a helmet.